An estimated 25-40% of U.S. pre-adolescents and adolescents are obese. Higher rates have been noted among minority youth. Onset of obesity in late childhood and early adolescence is associated with increased risks of "tracking" of obesity into adulthood, subsequent obesity-related morbidity and mortality, and obesity- related psychosocial morbidity. However, (l) we have limited ability to accurately identify those children who will become obese adults and those who will suffer obesity-related morbidities, (2) existing treatments for child and adolescent obesity have yielded modest, unsustained effects, and (3) single-component prevention interventions have been relatively ineffective. Therefore, we propose an integrated, multiple-component, school- and community-based intervention targeting both primary and secondary prevention of obesity among third- fourth-and fifth-graders ("School- and Family-Based Obesity Prevention for Children"). The proposed intervention model is derived from principles of Bandura's social cognitive theory, and includes activities in THE SCHOOL, THE HOME, and a clinically oriented component for HIGH-RISK CHILDREN. The school component includes: (l) A computer-based classroom curriculum, (2) A physical education curriculum and (3) A school lunch intervention. The home component includes correspondence materials and a videotape for parents. Children identified as "high risk" will be eligible to enroll in an intensive intervention. In addition, several innovative approaches will be included: interventions to influence food preferences and television viewing, interventions promoting health advocacy, and computer-assisted instruction. We propose an "efficacy trial" to evaluate the three-year intervention in a cohort of approximately 1200 3rd graders, in 14 ethnically diverse elementary schools, with follow-up in the 6th grade. 7 schools will be randomly assigned to the comprehensive intervention, and 7 schools will receive an attention-placebo classroom curriculum. Anthropometric measures and assessments of food preferences, cardio-respiratory fitness and self- reported behavior, attitudes and knowledge will occur every 6 months. Parent interviews will occur annually. Although a careful assessment of effects on parents and the schools will be done, the crucial question is whether the overall intervention has an impact on student adiposity and behaviors. The primary objective is to significantly reduce the prevalence of obesity, compared to controls, at the end of the three year intervention. Secondary objectives include maintenance of effects at 6-month follow-up, reducing obesity among high-risk children, improving cardio-respiratory fitness, increasing physical activity, decreasing sedentary activity, reducing the prevalence of unhealthful weight control methods, and improving knowledge, attitudes and perceived self-efficacy regarding the adoption of healthful behaviors. In addition, we will identify personal, behavioral and environmental (including family) factors prospectively associated with development of obesity, maintenance of normal weight, weight reduction among overweight children and obesity-related behaviors. Finally, we will examine longitudinal changes in height, weight, BMI, triceps skin fold thickness, and waist and hip circumferences in girls and boys. 8 - 12 years of age, with resect to stages of pubertal development.